323000332 - INTRODUCTION - VDC/ESP VEHICLE STABILITY CONTROL SYSTEM

CONSTRUCTION SPECIFICATIONS

VIEW OF ASSEMBLY1 - ABS/ESP control unit2 - Steering angle sensor3 - Engine management control unit4 - Yaw/lateral/longitudinal acceleration sensor5 - Right front wheel sensor6 - ASR off button7 - Right rear wheel sensor8 - Left rear wheel sensor9 - ESP warning light10 - EBD warning light11 - ABS warning light12 - Front wheel sensor Left13 - HHC warning light

SPECIFICATIONS

The BOSCH 8.1 ABS braking system currently used is the most advanced available to guarantee safe driving. To achieve this, an ESP system which includes ASR/MSR/HBA/HHC functions has been added to the ABS/EBD hydraulic control unit.µ - Wheel gripS - SlipA - EBD intervention areaA - ABS intervention areaC - ESP intervention area1 - Lateral force curve2 - Longitudinal force curveAs can be seen from the hold versus slip graph, the area covered by the ESP system is larger than that covered by a conventional ABS/EBD system.The ESP system switches on automatically when the vehicle is started up and cannot be switched off by the user; the button in the centre tunnel only switches off the ASR/MSR function and only when advisable (see ASR/MSR function).INPUT SIGNALS:- Wheel speed sensors (from direct line) (3)- Brake pedal sensor normally open (from direct line) (4)- Brake pedal sensor normally closed (from C-CAN line) (5)- ASR off button (from direct line) (6)- Engine management control unit (from C-CAN line) (2)- Throttle angle position (from NCM C-CAN line) (8)- Body computer (14)- Handbrake lever position (from C-CAN line)- Warning light status signal (from C-CAN line) (11)- Yaw sensor (Z) (rotation of vehicle on vertical axis) (from C-CAN line) (10)- Lateral acceleration sensor (Y) (from C-CAN line) (10)- Longitudinal acceleration sensor (X) (from C-CAN line) (10)- Steering angle/steering wheel rotation sensor (from C-CAN line) (12)- Robotised transmission control unit on versions where fitted (gear engaged status) (from C-CAN line) (13)- Hydraulic system pressure sensor (from direct line) (1)- Reverse gear engagement sensor (16)OUTPUT SIGNALS:- Brake pressure modulation control (15)- Ignition advance reduction control (from C-CAN line) (9)- Engine power management control (from C-CAN line) (8)- Gear change inhibition on versions with robotised gearbox (from C-CAN line) (13)- Wheel speed signal for speedometer and mileometer (from C-CAN) (14)- VSO signal (vehicle speed) (14)- ABS/ASR/ESP/HHC warning light in panel (from C-CAN line) (11)- ASR off LED (7)

ESP SYSTEM

Introduction

The ESP (Electronic Stability Program) is an active safety system for the control of the vehicle during dynamic manoeuvres, which intervenes in emergency conditions. The ESP system, as well as including the ASR/MSR/HBA/HHC functions described previously, keeps the vehicle stable in the event of brisk manoeuvres, especially on slippery surfaces. It reacts quickly to both vehicle oversteer and understeer, restoring stability and allowing the driver to maintain full control of the vehicle.    This has been achieved through the addition of special sensors: steering angle sensor and lateral acceleration/slewing sensor.The ESP system is managed by the A.B.S. electronic control unit, built into a special hydraulic control unit which allows action on the braking system, independent of the user''s action.The control unit processes the following signals:- steering angle/steering wheel rotation speed sensor- yaw/lateral/longitudinal acceleration sensor- motorised throttle position- wheel RPM sensors- hydraulic braking system pressure sensorand uses special algorithms in the electronic control unit software to obtain the figures for the dynamic control of the vehicle:- longitudinal and transverse slip between the wheels and the road surface- axle drift.Using these figures, the system interprets the effective dynamics of the vehicle; having identified all the critical conditions resulting from environmental factors (e.g. surface with poor grip) or any errors made by the user (e.g. panic situations) and with subsequent intervention on the brakes and the drive torque, the vehicle is restored to good driving conditions.The system interfaces with:- E.C.M. (Engine Control Module) for regulating drive torque,- MTA (robotized gearbox node) for the management of gear changes on versions where fitted- BCM (Body Computer Node) for the transmission of the vehicle speed and the control of the warning lights.The exchange of information between these components takes place via the C-CAN line.The C-CAN line is used to diagnose the system.The system is combined with a power unit with a specific brake pump; in addition, the pipes between the brake pump and the A.B.S. control unit have a flexible insert because the diameter of the pipe (6mm) is larger than regular pipes (4 mm); this is designed to prevent adverse effects on the operation of the ESP at low brake fluid temperatures.

Operating strategies

As described previously, in addition to controlling longitudinal vehicle slip, the ESP system also controls transverse slip and thus the vehicle''s lateral stability.The lateral stability of a vehicle depends on the reaction of the tyres to lateral forces, and on the adhesion force of the wheel to the road surface.It should be remembered that wheel grip depends on the vertical load and the wheel condition (loaded or unladen) and on the friction coefficient, which is in turn determined by the road surface and tyre conditions.When the vehicle is travelling in a straight line, the lateral forces do not really have an effect unless outside factors intervene (e.g. a gust of wind or a change to a different surface) and increase their intensity, unlike when driving round a bend where there is a strong increase in lateral forces due to the increase in centrifugal force.The action of the lateral forces produces a variation in the drift angle of the wheels and, consequently, a variation in the axle drift (drift angle = difference between the desired route and the actual route).The lateral forces do not, however, act equally on all four wheels because they are not subject to the same load conditions. In fact, the load on the wheel differs according to the situation the wheel is in, namely:- acceleration (lightening of the front axle and loading of the rear axle)- braking (loading of the front axle and lightening of the rear axle)- bend to the right/left (loading of the outer wheels and lightening of the inner wheels)- accelerating/decelerating round a bend (combination of the cases mentioned above).It is obvious that if the lateral forces acting on the individual wheels vary, there will also be a variation in the forces acting on the vehicle axles; consequently the lateral forces acting on the front axle overcome those on the rear axle and vice versa, determining a rotation (moment) on the vertical axis of the vehicle (yaw axis).The yaw moment affects the behaviour of the vehicle, producing either understeer or oversteer.UNDERSTEER:understeer for a vehicle is when, with increasing lateral acceleration, the drift angle for the front axle increases greatly compared with that of the rear axle. When this happens, the vehicle tends to go straight ahead (taking the curve wide) when cornering.OVERSTEER:oversteer for a vehicle is when, with increasing transverse acceleration, the drift angle for the rear axle increases greatly compared with that of the front axle. In this case the vehicle tends to turn around on itself (the rear axle tends to go straight on, causing the vehicle to cut the corner).To keep the effect of lateral forces under control and limit the yaw moment, the ABS control unit calculates the nominal behaviour of the vehicle by means of:- steering angle sensor- accelerator pedal position- brake pedal pressurethe control unit compares these parameters with the actual behaviour of the vehicle by means of:- vehicle speed sensor (active sensors on the wheels),- yaw/lateral acceleration sensorif the values differ from the normal operation of the vehicle, the control unit is capable of:- detecting actions carried out by the user, i.e. the steering wheel reveals the number of degrees (wide radius or narrow radius bends) and the rotation speed of the drive wheels (abrupt or gradual turns) and the throttle position and the brake pressure when accelerating or braking indicates how the user is taking the bend or deviating from a straight line.- detecting the actual behaviour of the vehicle given the environmental variables, e.g. slippery surface, gusts of wind, reaction of the vehicle to incorrect manoeuvres by the user, etc., in order to identify the yaw moment and the lateral sliding of the axles via the sensors on the four wheels and the yaw/lateral acceleration sensor.These operations are necessary to superimpose the mathematical model mapped in the control unit on the effective behaviour of the vehicle, in order to identify the vehicle''s state (understeer or oversteer) and to decide the action for the brakes and the engine managementUNDERSTEER ON CORNERSThe control unit detects the presence of understeer (mainly from the drift of the front axle), corrects the behaviour of the vehicle, braking the inner front and rear wheels round the bend in order to create an opposing moment which will lead the vehicle towards the centre of the bend and, possibly, reduce the drive torque.OVERSTEER ON CORNERSThe control unit detects the presence of understeer (mainly from the drift of the rear axle) and corrects the behaviour of the vehicle, braking the outer front wheel round the bend in order to create an opposite yaw moment. In certain cases, in addition to the action on the brakes, there is also an increase in the speed of the inner drive wheel round the bend.

The system intervenes before the oversteer and understeer values are too high, in order to prevent the countersteering manoeuvre from making handling difficult.

ABRUPT VARIATIONS FROM A STRAIGHT PATH (SLALOM/OVERTAKING)In the event of sharp variations from the path (e.g. overtaking, slalom), the control unit identifies possible oversteer and understeer conditions and corrects the path of the vehicle, acting as described previously.Sharp variation from the straight path (gusts of wind, driving on different surfaces)The control unit is capable of detecting deviations in the path and the prevalence of axle drift, and correcting the path through suitable action on the brakes and the engine.ABRUPT ACCELERATION/DECELERATIONThe control unit deploys the ASR/MSR strategy, while also controlling vehicle lateral acceleration and, as a result, the action on the brakes and drive torque.Exclusion of ASR/MSR systemIf the ASR/MSR function is cut out, the following functions remain activated:- ABS/EBD- T.C. up to a speed of 40 km- ESP with intervention of the brakes only- HHCESP INTERVENTION DISPLAYThe intervention of the ESP system is shown by the flashing of the special warning light on the instrument panel (5 Hz d.c. 50%).

the ESP system improves driving safety but there are limited situations which cannot be controlled by the ESP system. It is, therefore, not seen as a device which improves the vehicle''s performance, but as a device that improves its safety.

Asr/msr function

This system, in addition to the normal anti-lock and brake force distribution functions controlled by the ABS with EBD, also carries out the following functions:- acceleration slipping adjustment (A.S.R.)- adjustment of the engine braking torque (M.S.R.)- locking the differential through action on the brakes (T.C.).These functions are carried out through action on the drive torque (ASR/MSR) and the application of a braking force on one or both the drive wheels (TC).If, during acceleration, one or both the drive wheels tend to slip, the ASR system asks the engine management control unit to reduce the torque transmitted to the wheels. Almost simultaneously, it brakes the wheel or wheels without any intervention by the user (TC)If the wheels tend to lock during heavy deceleration, the MSR system requests that the engine management control unit adjusts the engine braking torque in order to prevent the vehicle becoming unstable.The system can be bypassed by operating the button on the dashboard next to the hazard warning lights button.The LED in the button comes on and the display in the instrument panel signals that the ASR/MSR system has been switched off.The warning light in the panel coming on indicates that the system is excluded on account of a fault recorded by the control unit.The intervention of the ASR/MSR is signalled by the flashing of the warning light in the instrument panel.Each time the vehicle is started up, the ASR/MSR function is activated even if the function was switched off when the vehicle was switched off.The system works through signals coming from the active sensors for the four wheels, from the brake light switch and from the ASR on/off button.It constantly compares the speed of the wheels on the same side of the vehicle (Right front with Right rear and Left front with Left rear) and when it detects a difference in speed, between the two wheels on the same side, of more than 2-6 km/h (intervention level) the ASR logic intervenes.The ABS/ASR control unit communicates continuously with the engine management control unit via the C-CAN line.Slipping of the drive wheelsIntervention - intervention times for good road grip conditionsDrive torque reduction by the engine management control unit through the alteration of the ignition advances, 6/100 of a second after the slipping limit is exceeded.A further reduction in torque through a decrease in the throttle opening (by the engine management control unit through the motorised throttle body after 15/100 of a second).Intervention of the hydraulic system (braking force on the drive wheels) after 2/10 of a second.Operation in poor grip conditionsThe system is capable of recognising these conditions by comparing

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